Conventional filament lamps, such as a halogen lamp, have been used for a long time as light sources for head lamps for vehicles, but long-life HID lamps, such as a metal halide lamp or the like, or LEDs with longer life and higher efficiency are also used in recent years.
In this way, advances in light source elements themselves have been made in order to increase the lifetime and the efficiency thereof, but the control of head lamp light beams merely involves primarily switching between a so-called high beam and a low beam (i.e., passing head lamp).
These days, however, researches are being carried out that aim to more finely control the head lamp light beams with the use of a light emitting element of, in particular, a solid state light source, and some proposals have been made.
For example, Japanese Patent Application Laid-Open Publication (Kokai) No. 2012-146621 describes a technique in which a hologram is illuminated by a semiconductor laser and a head lamp light beam having a desired light distribution is generated with diffracted light from the hologram.
This technique includes a proposal of enabling a different hologram to be selected from a plurality of holograms in accordance with the position at which the rotation is stopped, and also a proposal of disposing a liquid crystal prism that changes the direction of illumination light in accordance with an applied voltage and switching between a high beam light distribution and a low beam light distribution in accordance with the voltage.
Such technique, however, suffers from shortcomings that the only operation with high responsiveness is the switching between the high beam and the low beam and the selectivity from the plurality of holograms is low with only a limited number of options.
Also, Japanese Patent Application Laid-Open Publication No. 2013-125693 describes a technique of generating a headlamp light beam having a desired light distribution by scanning a white laser light beam generated by mixing laser light beams of three primary colors R, G, and B with the use of a two-dimensional galvanometer (or alternatively a polygon mirror) in order to improve the visibility.
This technique includes a proposal of enhancing, for example, the blue (or bluish) color in the illumination light at the shoulder of a road, and also a proposal of lowering the color temperature or illuminating a pedestrian with a more noticeable color in the case of a long drive or an elderly driver.
Such technique provides a desired light distribution through the two-dimensional scanning and may thus offer high degree of freedom in dynamically changing the light distribution condition or the like. However, the illumination laser light beam emitted at each moment as a head lamp light beam has a thin beam shape, and thus special measures for ensuring the safety need to be taken, which still remains as an unsolved problem.